This invention is generally directed to processes for the preparation of styrene butadiene resins. More specifically, the present invention is directed to processes for the preparation of styrene butadiene resins by dispersion polymerization methods. In one embodiment of the present invention, there is provided a process for the preparation of styrene butadiene copolymer resins by the polymerization of styrene and butadiene monomers in the presence of a steric stabilizer, wherein the stabilizer and monomers are soluble, and the copolymer formed is insoluble in the reaction medium. There is thus enabled with the process of the present invention styrene butadiene polymers which are useful as toner resins, and which resins need not be jetted. Some advantages of the process of the present invention include, for example, enablement of the direct preparation of toner size particles, that is those with an average diameter of from about 1 to about 15 microns, and preferably from about 3 to about 10 microns; narrow particle size distributions, that is with geometric standard deviations, GSD, of from about 1.0 to 1.4, and especially those with GSD of from about 1.0 to 1.1; broader molecular weight distributions in the polymer resulting in improved fusing properties; improved ability to initiate process changes enabling modification of the polymer properties for specific requirements; the avoidance of suspension failure; and the other advantages indicated herein.
The styrene butadiene polymers obtained with the processes of the present invention can be selected as resins for toner compositions, including magnetic, single component, two component, and colored toner compositions. There are also provided in accordance with the present invention positively or negatively charged toner compositions comprised of styrene butadiene resin particles obtained by the dispersion polymerization processes illustrated herein, pigment particles or dyes, and optional additive components such as metal salts of fatty acids, colloidal silicas, waxes with hydroxyl functionality, and charge enhancing additives. The toner, and developer compositions illustrated herein are useful in electrophotographic imaging systems, especially xerographic imaging methods. In addition, developer compositions comprised of the aforementioned toners and carrier particles can be formulated.
Copolymers of styrene and butadiene may be prepared by various techniques, reference U.S. Pat. No. 4,469,770. Emulsion polymerization is believed to be the most popular polymerization process selected for the preparation of the aforementioned copolymers. However, emulsion polymerization processes have a number of disadvantages, including for example the presence of undesirable residual contaminants in the emulsion polymerization process. For example, the presence of ionic surfactants, such as sodium dodecylbenzene sulfonate, during emulsion polymerization may adversely affect the electrical properties of electrostatic toners prepared with these materials. In addition, emulsion polymerization techniques generate particle sizes (average particle diameter), usually less than one micron, which particles are of insufficient size to permit their direct utilization as toner compositions.
Suspension polymerization processes may also be selected to prepare copolymers of styrene and butadiene. For example, U.S. Pat. No. 4,558,108 discloses a suspension stabilizing agent such as tricalcium phosphate to prevent particle agglomeration. However, the aforesaid polymerization processes are susceptible to suspension failure. With failed batches, the poorly suspended particles coalesce into a single lump of polymer, leading to bulk polymerization. This adversely affects heat transfer, molecular weight and monomer conversion resulting in materials that are unsuitable as toner resins. In suspension polymerization, the surfactant to water ratio, tricalcium phosphate to monomer ratio, source and purity of tricalcium phosphate, and the presence of other additives such as chain transfer agent or crosslinking agent are of importance to suspension stability. In addition, stirring too slow or too fast can also cause suspension failure. The present invention avoids the need for formation of a suspension thereby eliminating the danger of suspension failure. A further advantage of the process of the present invention is the ability to synthesize toner sized particles, whereas with suspension polymerization processes there are usually generated particles of an average diameter of from about 200 to about 2,000 nanometers. Another advantage associated with the process of the present invention resides in the ability to synthesize monodispersed particles, that is those with a very narrow size distribution possessing, for example, a GSD of from about 1.0 to 1.1. Such a narrow size distribution is advantageous since all the particles are substantially the same size, therefore, there are substantially no particles significantly larger or smaller than the average size, whose preferential development can cause with usage modifications in the toner triboelectric characteristics and the developed density.
In Hong U.S. Pat. No. 4,607,058, there is disclosed vinyl or ethylenic polymerization in the presence of a dispersant, preferably a hydroxypropylmethylcellulose polymer with a molecular weight of 50,000 to 500,000, in an aqueous vehicle. This patent disclosed refers to suspension polymerization processes, that is the monomer selected is insoluble in the solvent (water). In contrast, the process of the present invention is directed to dispersion polymerization, that is where the monomer or monomers are soluble in the reaction medium. Further, the monomer of the '058 patent is usually present in the form of droplets, which causes suspension failure, while with the process of the present invention the monomer or monomers are molecularly dissolved in the solvent. Furthermore, the '058 patent process appears to occur in water only. Moreover, the process of the '058 patent generally yields particles with a size of 30 to 1,000 microns (typically 120 microns), while with the process of the present invention there are usually provided smaller particles, that is with an average diameter of from about 0.1 to about 200 microns particles, and typically from about 5 to about 10 microns, which are of more interest to us. The difference in size range results, it is believed, since the size of the particles of the '058 patent are determined by the droplet size, while with the process of the present invention, particle size is usually dependant upon the solvent selected, the concentration and molecular weight of the steric stabilizer, monomer concentration, the dynamics of the reaction/agglomeration of the polymer, and other factors. Additionally, with the process of the present invention grafting and steric stabilization are permitted. The term dispersion is utilized in the aforesaid '058 patent with reference to the initial monomer water mixture, reference column 1, line 10, however, such a reference is not directed to, it is believed, dispersion polymerization as illustrated with reference to the process of the present invention. Also, the term dispersion, for example, has been applied to multiphase mixtures such as those employed in suspension polymerization. Other patents of interest include U.S. Pat. Nos. 3,346,520; 3,560,418; 3,941,729; 4,345,056 and 4,739,023.
Developer and toner compositions with certain waxes therein are known. For example, there are disclosed in U.K. Patent Publication 1,442,835 toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to 6,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes. Additionally, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374, the disclosure of which is totally incorporated herein by reference. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference Palmeriti et al. U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms; or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43. Toner and developer compositions with styrene butadiene polymers are also disclosed in application U.S. Ser. No. 081,261, (now abandoned) the disclosure of which is totally incorporated herein by reference.
Illustrated in U.S. Pat. No. 4,883,736, the disclosure of which is totally incorporated herein by reference, are toner and developer compositions with linear polymeric alcohols comprised of a fully saturated hydrocarbon backbone with at least about 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group, which alcohol is represented by the following formula: EQU CH.sub.3 (CH.sub.2).sub.n CH.sub.2 OH
wherein n is a number of from about 30 to about 300, and preferably of from about 30 to about 100, which alcohols are available from Petrolite Corporation, and wherein the toner may contain styrene butadiene resins. Particularly preferred polymeric alcohols include those wherein n represents a number of from about 30 to about 50. Therefore, the polymeric alcohols selected have a number average molecular weight as determined by gas chromatography of from about greater than 450 to about 1,400, and preferably of from about 475 to about 750. In addition, the aforementioned polymeric alcohols are present in the toner and developer compositions in various effective amounts, and can be added as uniformly dispersed internal, or as finely divided uniformly dispersed external additives. More specifically, the polymeric alcohols are present in an amount of from about 0.05 percent to about 20 percent by weight. Therefore, for example, as internal additives the polymeric alcohols are present in an amount of from about 0.5 percent by weight to about 20 percent by weight, while as external additives the polymeric alcohols are present in an amount of from about 0.05 percent by weight to slightly less than about 5 percent by weight. Toner and developer compositions with the waxes present internally are formulated by initially blending the toner resin particles, pigment particles, and polymeric alcohols, and other optional components. In contrast, when the polymeric alcohols are present as external additives, the toner composition is initially formulated comprised of, for example, resin particles and pigment particles; and subsequently there are added thereto finely divided polymeric alcohols. The aforementioned alcohols can also be selected as optional additives for toner compositions containing the styrene butadiene resins obtained by the processes of the present invention.
Furthermore, references of background interest are U.S. Pat. Nos. 3,165,420; 3,236,776; 4,145,300; 4,271,249; 4,556,624; 4,557,991; and 4,604,338.
Moreover, toner and developer compositions containing charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well know. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Further, there are illustrated in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer and toner compositions having incorporated therein as charge enhancing additives, organic sulfate and sulfonate compositions; and in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride.
Other prior art disclosing positively charged toner compositions with charge enhancing additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; and 4,394,430.